The overall objective of this project is to develop a new understanding ofthe microenvironment that supports the growth, survival and migration of astrocytoma cells, and thereby identify new therapeutic approaches. In preliminary studies we have shown that human astrocytoma cells do not grow indiscriminately within the brain parenchyma, but prefer to grow in particular microenvironments. In the proposed studies we will use primary cultures from patient samples to determine whether astrocytomas are addicted to the environment of the brain region in which they developed, and to define cellular mechanisms by which the tumor microenvironment promotes tumor maintenance. We have three aims: Aim One: Determine whether pediatric astrocytomas are addicted to the particular location in which they originated. We will use a new slice overlay assay, to determine whether i) forebrain tumors preferentially grow in the specialized microenvironment of the forebrain; ii) hindbrain tumors preferentially grow in the cerebellum and brainstem areas ofthe hindbrain; iii) BRAF overexpression, a characteristic feature of cerebellar pilocytic astrocytomas, specifically facilitates growth of neural precursor in the cerebellar microenvironment. Aim Two: Define the cellular basis ofthe microenvironment While the microenvironment is clearly important for tumor growth and maintenance, the reason why tumor cells are preferentially found in particular locations is not understood. We will determine whether i) the microenvironment stimulates tumor proliferation; ii) the microenvironment selectively promotes tumor cell survival; iii) tumor cells preferentially migrate towards this microenvironment. Aim Three: Determine whether primary cilia coordinate the tumor cell response to its microenvironment. Our preliminary studies indicate that many astrocytoma samples exhibit primary cilia, visualized with antibodies to acetylated tubulin or adenylate cyclase 3. To determine whether primary cilia are signaling organelles that contribute to growth of astrocytomas, we will determine whether i) Primary cilia are preferentially found on higher grade tumors; ii) Primary cilia point towards the vasculature; iii) components of critical growth pathways localized to cilia of tumor cells; iv) Primary cilia are required for tumor growth.